Does Ammonia Released from Protein-Based Attractants Modulate the Capture of Anastrepha obliqua (Diptera: Tephritidae)?

SIMPLE SUMMARY: The West Indian fruit fly, Anastrepha obliqua (family Tephritidae), is an important pest of mango and guava in the Neotropical region. Previous studies have indicated that ammonia is involved in fruit fly attraction to sources of food, particularly if protein is present. In laboratory experiments, flies were attracted to ammonia solutions of increasing concentration. In contrast, fly captures by different protein-based attractants were not related to the quantity of ammonia released by the attractant. Flies also responded differently to yeast suspensions of different alkalinity that released different amounts of ammonia. In field experiments, flies were strongly attracted to yeast in ammonia solutions after 24 h, but this effect did not persist when measured over a 7-day period. We conclude that A. obliqua flies are attracted to ammonia solutions in the absence of other stimuli, but attraction to protein-based attractants or alkaline yeast suspensions is not correlated with the quantity of ammonia released by these substances. Ammonia is an important component in fruit fly attraction, which also seems to depend on the presence of other compounds derived from protein food sources in different stages of decomposition. ABSTRACT: Tephritid fly responses to food-based attractants involve a complex range of food-derived semiochemicals, including ammonia. We performed laboratory and field experiments to compare the attraction of Anastrepha obliqua (Macquart) to ammonia with the attraction to commercial food attractants and torula yeast at a range of pHs. A positive correlation was established between the concentration of ammonia in solution (1.5–150 mM ammonium solution) and gaseous ammonia released by bottle-type traps. This resulted in an asymptotic response in captures of A. obliqua flies in traps that released 99–295 µg ammonia/h. Pairwise comparisons in laboratory cages revealed that traps baited with 150 mM ammonia solution captured similar numbers of A. obliqua as traps baited with Biolure 2C, CeraTrap, and hydrolyzed protein products (Captor, Winner, and Flyral) plus borax, despite the low quantities of ammonia (11–56 µg/h) released from these attractants. Subsequent choice experiment captures in traps containing ammonia solution were similar or higher than those of commercial attractants, with the exception of Winner + borax, but were not correlated with the ammonia released from attractants. Captures of flies in traps containing ammonia solution were increased by the addition of 1% torula yeast or torula yeast alkalized with sodium hydroxide or borax despite differences in the quantities of ammonia released. Fly captures generally increased with increasing alkalization of torula yeast (pH 7.5–9.5). In the field, torula yeast in ammonia solution captured similar numbers of A. obliqua flies as Captor + borax when traps were evaluated after 24 h but not after a 7-day trapping period. Traps baited with ammonia solution or Winner + borax were significantly less attractive than Captor + borax in both field experiments. We conclude that A. obliqua flies are attracted to ammonia solutions of increasing concentration, up to 150 mM, in the absence of other stimuli, whereas attraction to commercial attractants or alkalized torula yeast is not correlated with the release of ammonia.